Commercial “bag house” type filter installations typically consist of a plurality of parallel filter units, each containing a plurality of parallel rows of vertically arranged filter elements in the form of filter bags. Each such filter bag has a top end opening. A gas polluted with particulates is channeled through the filter installation's filter units to filter and collect the particulates entrained in the gas. By filtering and collecting the particulates entrained in the gas, a cleaned gas is produced. More specifically, a cleaned gas is produced by channeling polluted gas into a filter installation for passage through one or more filter units arranged for gas flow from an exterior surface of a plurality of filter bags through to an interior area within the filter bags via gas movement through the sides of the filter bags. In passing from an exterior surface of the filter bags through to an interior area within the filter bags, particulate pollutants carried by the gas become trapped on the exterior surface of the filter bag. Hence, gas in the interior area of the filter bags is the so produced “cleaned gas”. Cleaned gas exits the interior areas of the filter bags via a top end opening formed in a top of each such filter bag. As such, cleaned gas flows from the top end openings through an outlet duct common to the filter units.
During operation of the filter installation, a negative pressure is typically generated by a fan arranged downstream of the filter installation causing gas flow through the filter units and filter bags. As the gas passes through the sides of the plurality of filter bags, the gas is cleaned as dust and particulates entrained in the gas deposit on the exterior surfaces of the filter bags forming a dust cake. Cleaning of the filter bags to remove dust cakes is necessary for effective equipment operation and performance.
Cleaning of the filter bags is accomplished using a pressure medium in the form of compressed air pulses injected into the filter bags in a direction opposite to that of gas filtering. The rows of filter bags are cleaned successively using compressed air pulses generated and transmitted at the same time to all filter bags in a given row. Such is accomplished by means of a cleaning unit arranged for successively cleaning each individual row of filter bags. Each cleaning unit comprises a nozzle pipe arranged above and extending along the length of the associated row of filter bags parallel thereto for cleaning thereof. Each nozzle pipe also includes a distribution pipe with a plurality of vertically downwardly projecting pipe sockets connected thereto with each individual pipe socket positioned straight above a filter bag top end opening in the row. The function of these pipe sockets is to direct via nozzles compressed air pulses into each of the respective filter bag top end openings. The pipe sockets usually have a diameter of about 1.5 to 2 times greater than the diameter of the nozzle associated therewith. The nozzles associated therewith consist of circular holes of varying diameter formed in the distribution pipe. The varying diameters of the circular holes in the distribution pipe are determined empirically based on the total number of pipe sockets/nozzles along the length of the distribution pipe requiring a uniform distribution of compressed air pulsed therethrough. As such, circular holes arranged in the distribution pipe a greater distance from the nozzle pipe are larger in diameter than those of circular holes arranged in the distribution pipe a lesser distance from the nozzle pipe. By so varying the diameter of the circular holes, a uniform distribution of compressed air pulsed therethrough is achieved.
In the cleaning of filter bags using a pulse of compressed air, a valve is temporarily opened to establish a connection between a compressed air tank and the nozzle pipe to transmit a compressed air pulse through the nozzle pipe and its associated distribution pipe, pipe sockets and nozzles. As such, a single compressed air pulse is supplied to each of the filter bags in a row relatively simultaneously. Nozzle pipes as described above are thus used to effectively and efficiently clean individual rows of filter bags with compressed air pulses. In cleaning, compressed air pulses dislodge dust and particulates that collect and cake in and on the walls of the filter bags. Dust cakes that form on the filter bags are thereby loosened by the compressed air pulse moving from the interior area of the filter bags, through the filter bag side walls and out of the filter bags to an area in the filter unit exterior thereto. The resultant loosened dust cakes fall off the exterior of the filter bags for hopper collection.
In operating a cleaning unit, it is essential that the above-described pulse valve delivers a cleaning pulse of compressed air at a relatively high pressure with a relatively low consumption of compressed air. Pulse valves function by a cavity behind a plunge or membrane emptying through either a solenoid valve or a pilot valve, whereby the plunge or membrane is displaced with rapid acceleration due to the differential pressure between an air tank pressure on one side of the plunge or membrane and the cavity pressure on the other side of the plunge or membrane. The plunge or membrane is displaced with considerable velocity as a result of the pressure differential and eventually hits an end position with very high momentum. The plunge or membrane hitting the end position with very high momentum creates a significantly loud noise upon impact. Likewise, when the plunge or membrane hits the end position, the impact thereof creates relatively high mechanical stresses. Mechanical stresses on the valve shorten the operational life expectancy of the valve and add to the system's operation costs when performance is hampered and/or replacement is necessary. Further, the plunge or membrane typically bounces with several pressure peaks upon hitting the end position causing compressed air waste. Hence, to increase system performance and decrease system operational costs, a valve with decreased mechanical stresses, decreased operational noise, decreased compressed air waste and increased operational life expectancy is desired.